i get different negative values too And. but 0 and positive figures match so i'm not bothered

 

1 bar is 14.5 psi, so your calculation is correct. The readings will depend on your altitude and the weather.

d

 

Say wouldn't it have been easier to just directly convert the voltage into 4 bar?

So lesse quick formula would be.

5 volts equivalent to 255 x (x/255 = volts)
Sensor range 0 to 5 volts so whole range used. (no offset)

BAR = x/((255*5)/4) = x / 318.75

If you wanted 0 bar to be atmosphere pressure you could just subtract 1 at this point

 

It is offset.

d

 

Thats news to me what were the voltage ranges?

 

From the omnipower directions:
--
P= pressure in KPA 4 bar = 400 KPA

Voltage out/signal = 5 X (.002421 X P - .00842)

Atmosphere equals 1 bar or 100 KPA = 5 X (.002421 X 100 - .00842) = 1.168 volts @ 1 bar or 100 KPA

--

That's why I posted a corrected formula way back at the beginning of this thread. The one in mrfred's post is slightly off.

d

 

Ah thats really interesting i thought the sensors weren't offset like that.

 

That was the point of post #43. A lot of folks seems to be using an incorrect scaling. Oh well...

d

 

Doesn't seem to be offset by much though correct? looks like .5 psi or so?

 

Yep.

d

 

Although it may be only a small offset, do we change all 3 scalings to something like these?

PSI8a Omni 4 bar =

ROM to Display = x*0.2340/2+0.5043
Display to ROM = (x-0.5043)/0.2340*2

PSI16a Omni 4 bar =

ROM to Display = x*0.2340/2+0.5043
Display to ROM = (x-0.5043)/0.2340*2

BoostErrorPSI Omni 4 bar = (Assuming ~0.5 psi offset is eliminated by substracting two PSI values)

ROM to Display = (x-128)*(0.2340/8)
Display to ROM = x/(0.2340/8)+128

Also EVOscan formula is now changed to =

0.2340*x + 0.5043 - 14.7

(Assuming 14.7 psi atmosphere pressure)

?

 

are these the values I should now be using?
thanks

 

Why are the settings for the JDM MAP (3 bar) and Omni 4 bar the same?

MAP Test 1: Mid VE High Voltage Test -- Change from 4.61 volts to 4.90 volts.
MAP Test 1: Mid VE Low Voltage Test -- Change from 0.10 volts to 0.06 volts.
MAP Test 3: High VE Voltage Test -- Change from 1.80 volts to 0.51 volts.

 

Those tests are for when the sensor goes out of range like unplugging it, shorting it, etc. It doesn't really do much else :P.

 

RoadSpike,
Thank you. I understood everything.
Another question: what else can I do with Omni 4 bar sensor and the stock ECU?

By what formula to Evoscan 2.7 to calculate the pressure in the bar?